1. Field of the Invention
The invention relates to a vehicle braking/driving force control system and vehicle braking/driving force control method that individually control driving force or braking force to be generated by each wheel of the vehicle.
2. Description of Related Art
In recent years, there has been developed a so-called in-wheel motor-type vehicle as one mode of an electric vehicle. In the in-wheel motor-type vehicle, an electric motor (motor) is arranged inside or near each wheel, and each wheel is directly driven by the electric motor. In the in-wheel motor-type vehicle, electric motors provided respectively for wheels (drive wheels) are individually subjected to rotation control, that is, the electric motors are individually subjected to power running control or regenerative control, to individually control driving torque or braking torque applied to each drive wheel to thereby make it possible to appropriately control the driving force and braking force of the vehicle in response to a running condition.
Then, there has been suggested a control system that uses the function of individually controlling driving torque or braking torque applied to each driving wheel in this way to suppress a change in the behaviors of a vehicle body. For example, Japanese Patent Application Publication No. 2007-110836 (JP-A-2007-110836) describes a vehicle braking/driving force control system that applies different braking/driving forces to respective driving wheels to control pitch moment and yaw moment generated about the barycenter of the vehicle in order to suppress vibrations of the vehicle in the vertical direction (pitch rate) resulting from the pitch behavior that occurs when the vehicle runs over a step, or the like, of a road surface and to stabilize the yaw behavior in the yaw direction. In addition, JP-A-2007-110836 describes a vehicle control system that independently controls braking/driving force of each driving wheel to control the roll behavior of a vehicle body. Furthermore, Japanese Patent Application Publication No. 2006-109642 (JP-A-2006-109642) describes a vehicle braking/driving force control system that individually controls the braking/driving force of each wheel to control the bouncing behavior of a vehicle body.
Incidentally, in the above control systems, the driving force or braking force of each driving wheel is controlled to control the behaviors of the vehicle body (sprung mass) arranged on springs, that is, on suspension mechanisms utilizing suspension reaction force generated by the suspension mechanisms. However, the above control systems each control only a single behavior, that is, a pitch behavior, a yaw behavior, a roll behavior or a bouncing behavior. In this case, when driving force or braking force of each driving wheel is controlled, that is, a driving force allocation is controlled, to, for example, control the pitch behavior or the roll behavior while controlling the yaw behavior, control of each of these behaviors may influence another behavior. Thus, in the case where the yaw behavior, the pitch behavior and the roll behavior each are independently controlled, it is difficult to control the behaviors at the same time only by a simple combination of these controls, so a favorable ride comfort may not be obtained.